If $h_i$ are consistent and admissible, are their sum, maximum, minimum and average also consistent and admissible?
The issue is that you must include assumptions about hopping into your heuristic. In particular, if you are considering individual cars then you must assume that they might be able to hop all of the way to the goal. Thus, your heuristic for each car should be Manhattan distance divided by 2. That's guaranteed to be admissible when you take the max.

If you consider all possible cars you can do better, but you'll need to reason out all the cases. (In general every car either waits or moves, and for every waiting car one car can hop. So, by looking at the minimum distance for any car to reach the goal you can start to reduce your heuristic.) But, that is a different question.